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Friday, June 7, 2013

ISTANBUL — The use of larger head sizes and resurfacing of metal-on-metal hip prosthesis has become an increasingly important issue as indicated by metal-on-metal hip findings in the National Joint Registry of England, Wales and Northern Ireland and biomechanical studies of friction conducted in Germany.

But that is not the only problem, according to two presenters at the 14thEFORT Congress.

"There is no conclusive evidence that resurfacing or metal-on-metal gives better functional results," Ashley Blom, MBChB, MD, PhD, FRCS, FRCS(Tr & Ortho), of Spire Bristol Hospital, Bristol, United Kingdom, said. He discussed the most pertinent and recent results for these prostheses in the National Joint Registry of England, Wales and Northern Ireland (NJR).

Ashley Blom

The use of metal-on-metal (MoM) hip replacement has been especially problematic in women aged 55 years or older, based on NJR data he reviewed.

"Resurfacing has a massive failure rated compared to alternatives" particularly when surgeons performed the procedures with the ASR prosthesis (DePuy; Warsaw, Ind., USA), Blom said.
Citing a study where he and colleagues compared patients with MoM arthroplasty to a controlled population in the UK Hospital Episode Statistics database, Blom said although the model used is imperfect, "MoM does not lead to an increased incidence of cancer in the short-term." But because some cancers take time to develop, "We need to repeat this study every 5 to 10 years in this cohort."Michael M. Morlock, PhD, of Institute of Biomechanics, Hamburg, Germany, discussed the consequences of friction with large femoral heads in MoM hip arthroplasty during the session, which was organized by the European Orthopaedic Research Society. "Large heads were introduced in order to deal with the dislocation problem in total hip arthroplasty. This was done without realizing that large heads carry certain disadvantages with respect to increased friction and require even more adequate cup positioning than smaller heads in order to function properly and achieve good tribological behavior," Morlock said.

Michael M. Morlock

When it comes to increased in vivo friction in MoM hip arthroplasty, "It is not just the head size itself. It also has something to do with the cup position," he said.

He addressed factors that affect friction, including some that Sir John Charnley personally analyzed 50 years, including the role of lubrication and material hardness.

Morlock also described MoM hip arthroplasty taper wear as a high frictional problem that "we have not seen coming."

It will likely be one that is discussed for the next 10 years, he said.

Disclosures: Blom is on the speaker’s bureau for Stryker and receives research support or is a principal investigator for DePuy Synthes and Stryker. Morlock is a consultant to, on the faculty of, and/or receives institutional support from Aesculap, Ceramtec and DePuy Synthes.